Die casting



Dec. 19, 1933. w. P. SHERMAN 0,

DIE CASTING Filed Dec. 1, 1951 g Sheets-sheet 1- JNVEN TOR. ML 7:7? 2 SHERMAN ORNEYS.

Patented Dec. 19, 1933 UNITED STATES PATENT OFFICE Application December 1,

10 Claims.

This invention relates to die casting, and more particularly to die casting machinery of the hydraulic or hydrostatic pressure operated type.

In a die casting machine of the hydraulically operated type, it is frequently necessary to use a piston and cylinder of relatively large diameter in order to open and close a separable die. The separable portions of the die must be relatively moved for a considerable distance, but this movement requires a force which is very small indeed compared with the pressure which must be exerted against the die portions to keep the same tightly closed when the molten metal is being forced into the mold impression under high pressure. It is necessary either to limit the permissible parting face area of the mold impression in the die, or to use a die operating piston of excessively large diameter, and in either case considerable waste of hydraulic power results because of the large volume of high pressure fluid used for opening and closing the die.

To overcome the foregoing difliculties and to operate a hydraulic piston with considerable saving in power, I employ a pressure booster or differential hydraulic piston comprising connected pistons of small and large diameter, and ,7 I connect the high pressure side of the booster to the die operating cylinder and admit pressure fluid from the single source of pressure fluid to the low pressure side of the booster, thereby developing and forcing a quantity of extra high pressure fluid into the die closing cylinder.

The extra high pressure for the die closing cylinder is needed only at the time of injection of molten metal into the die. The molten metal is ordinarily forced into the die under pressure by utilizing a fluid pressure medium. This is generally true regardless of whether the metal is transferred by means of an enclosed gooseneck ladle machine or an immersed or submerged plunger machine or a ladle-filled cup and plunger machine. A further object of the present invention is to provide for proper timing and interrelation of the steps in the operation of the die casting machine, particularly with a view to insuring the application of extra high pressure fluid to the die closing cylinder at the time of injection of metal into the die, and with a further object in view of simplifying the valve operating mechanism needed to attain these ends and, in fact, even to dispense with special valve mechanism, so that the pressure booster device of my invention may be applied to existing die casting machines as an auxiliary or accessory attachment. To fulfill these desiderata, I con- 1931. Serial No. 578,306

nect the low pressure side of the booster to the supply line leading to the cylinder which operates the plunger for transferring molten metal into the die, or, more generically, I connect the low pressure side of the booster to the pressure 0 supply line for whatever means is employed to force metal under pressure into the die. It will at once be evident that upon admission of pressure fluid to this supply line in order to transfer metal into the die, there is a simultaneous actug5 ation of the booster, causing an application of maximum closing pressure on the die during the casting operation.

To the accomplishment of the foregoing and such other objects as may hereinafter appear, my invention resides in the die casting machine elements and their relation one to the other, and the method of operating the same, as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by drawings, in which:

Fig. 1 is a partially sectioned side elevation of one form of die casting machine with the valve mechanism and pressure booster therefor schematically connected in circuit;

Fig. 2 is a side elevation of power driven valve mechanism for the die casting machine;

Fig. 3 is a front elevation of the said valve mechanism; 5

Fig. 4 is a plan view of a modified form of valve box; and

Fig. 5 is a further modification showing hydraulic mechanism for partially controlling the operation of the valve system. I

Referring now to the drawings, and particularly to Fig. 1 thereof, the die casting machine there shown has mounted therein a separable die consisting of a stationary portion 2 and a movable portion 4, the opening and closing of which is controlled by means of hydraulic piston and cylinder mechanism 6 and 8. A pressure tank or source of pressure fluid is connected to the valve box 10 through a supply pipe 12, and the pressure fluid is fed through pipe 16 to the die operating cylinder 8 under control of the valves in valve box 10. After the die 2, 4 has been closed and at the time of the casting operation itself, a source of extra high pressure fluid 18 is connected to cylinder 8 in order to keep the die 2, 4 closed under maximum obtainable force.

In order to simplify the mechanism and apparatus needed for practicing the invention, and particularly in order to dispense with the necessity of providing a complete super-pressure sys- 10 tem including a supply tank and machine for keeping the same under maximum pressure, I prefer to generate or develop the extra high pressure fluid by utilizing some of the normal or moderate pressure fluid. Accordingly, the source of extra high pressure fluid 18 consists of a pressure booster or differential piston mechanism including a low pressure cylinder 20 as well as the high pressure cylinder 18. The high pressure cylinder 18 is provided with a piston 22 of relatively small diameter, while the low pressure cylinder 20 is provided with a piston 24 of relatively large diameter. The pistons 22 and 24 are preferably directly connected together, as shown. The space between the cylinders 18 and 20 is preferably vented, as is indicated at 26, in order to prevent building up of pressure therein. It will be evident that by connecting the low pressure cylinder 20 through pipe line 28 to the regular pressure tank, an extra high pressure may be built up in cylinder 18 and applied to the die closing cylinder 8 at the end of the closing stroke of piston 6, at which time only an exceedingly small quantity of the extra high pressure fluid is needed to maintain the desired force on the die.

Considering the die casting machine in greater detail, it may first be stated that the particular machine shown has been selected solely by way of exempliflcation, and that the invention is applicable to all types of hydraulically operated die casting machines. In the present disclosure, I employ the term hydraulic as being synonomous with hydrostatic, and it is to be understood that the pressure medium employed may be any fluid desired, including such widely different fluids as oil and air as well as water. The particular machine here shown is preferably operated by means of compressed oil, and corresponds to that disclosed in my copending application for Die casting machine, Serial No, 577,019, flled November 24th, 1931.

In the said copending application, it is explained that the advantage of being able to cast any metal under any desired pressure is obtained by utilizing a pressure receptacle or cup 30 into which a single measured charge of molten metal is ladled. Aplunger 32 is reciprocable into and out of the cup 30, and when moved downwardly, forces the charge of molten metal from cup 30 through tapered or diverging gate 34 into the mold impression 36 in the die 2, 4. The lower end of plunger 32 is cut away, as is indicated at 38, in order to provide a clearance for permitting free flow of metal from cup 30 upwardly into gate 34. After the casting operation has been completed, the plunger 32 is retracted and the solidified residue of metal in cup 30 must be removed, which is preferably accomplished by suitably keying or dovetailing the residue of metal in the plunger 32, as by means of a transverse slot 40. The solidified residue of metal in cup 30 is thus sheared from the solidified residue of metal in gate 34, and is removed from the cup with the plunger, after whichit is removed from the plunger and remelted and reused.

Meanwhile, die 2, 4 is opened by moving the ejector half 4 of the die to the right or away from the cover portion 2 of the die. The casting moves with the ejector die and draws the solidified metal from gate 34 with it. Near the end of the opening of the die, appropriate ejector pins and ejector plate mechanism of conventional type housed in die box 42 come into action and force the flnished casting from the mold impression in ejector die 4. It will be understood from the drawings that the complete ejector die 4, 42 is mounted on a platen 44 reciprocable on tension and guide rods 46, and that the platen 44 is itself reciprogated by die operating piston 6 sliding in cylin- Plunger 32. is operated by hydraulic piston and cylinder mechanism 48, 50. The control of the flow of pressure fluid between the regular pressure tank and the cylinders 8 and 50 is preferably by means of valve mechanism such as that schematically shown .in valve box 10. In order to simplify the necessary valve mechanism, the inner ends of cylinders 8 and 50 are preferably permanently and continuously connected directly to the pressure tank, as by means of the pipes 52 and 54 respectively. The areas of the inner sides of pistons 6 and 48 are reduced to a minimum value needed for opening the die 2, 4 or for elevating the plunger 32. This continuous force" is directly opposed and overcome when pressure fluid is admitted to the outer ends of cylinders 8 and 50 through pipes 56 and 58 respectively.

Attention is now directed to valve box 10. This valve box or look is provided at its nearer end with an inlet or pressure valve 60 and an exhaust or discharge valve 62 for controlling the operation of die closing piston 6. It is further provided at its remote end with a similar inlet or pressure valve 64 and an exhaust or discharge valve 66 for controlling the operation of plunger operating piston 48. The valves may be conventional, and are shown schematically and not to scale merely to show their relation to the complete combination. The valves are preferably constructed as balanced valves. Valve 60, for example, includes a valve disc 68 and a piston 70. The pipe 12 communicates with an intermediate chamber 72. Upward or opening movement of valve 60 connects chamber 72 with an upper chamber 74. The latter is permanently connected by a suitable small passage, not shown, with the lower or bottom chamber 76.

Valve 62 is generally similar to valve 60, but in this case the valve disc 78 is located below counter-balancing piston 80, and acts to connect the intermediate chamber 82 with bottom cham ber 86, which in turn is connected by means of a passage, not shown, with top chamber 84. The

bottom chamber 86 is connected through a pipe 88 to an exhaust or low pressure tank, from which the oil may again be pumped by a suitable compressor to the high pressure tank to which the pipes 12, 52, and 54 are all connected.

Upper chamber 68 and intermediate chamber 82 are both connected through a pipe 90 to pipe 16 which in turn connects with pipe 56 and cylinder 8. It will be evident from an inspection of the valve system that when valve 60 is elevated, the pressure fluid flows from the pressure tank to cylinder 8. At the end of the die casting operation, valve 60 is closed and valve 20 is open, thereby permitting the fluid to be discharged from cylinder 8 to the exhaust tank. The intermediate chamber 72 and the bottom chamber 86 extend through the valve block 10 to valves 64 and 66. By direct analogy, it will be understood that when valve 64 is opened, pressure fluid is admitted from the pressure tank through pipe 92 to pipe 58 and cylinder 50, and that on the other hand, when valve 64 is closed and exhaust valve 66 is opened, the fluid is discharged from cylinder 50 to the exhaust tank through pipe 88. In each case the valves may be balanced as desired, but for reasons next explained in connec-.

tion with Figs. 2 and' 3 of the drawings, the valves are preferably slightly unbalanced so as to tend to remain closed, or in lieu of such unbalance, appropriate spring mechanism or other device is employed to tend normally to keep all of the valves 60, 62, 64, and 66 in their closed condition.

Referring now to Figs. 2 and 3, the valve block 10 corresponds to that shown in Fig. 1, and is similarly provided with valves 60, 62, 64, and 66 (the latter not being shown). The pipes 12 and 88 are connected to the pressure and exhaust tanks respectively, and the pipes 90 and 92 are connected to the die operating cylinder 8 and plunger operating cylinder 50 respectively, and correspond to those shown in Fig. 1. The valve block 10 is mounted on a frame 100 which carries a cam shaft 102 on which four cams 104 are mounted. The cams cooperate with cam followers 106 which intum, through levers pivoted on a shaft 108, operate the valves 60, 62, 64, and Cam shaft 102 has mounted thereon a sprocket gear 110 meshing with a sprocket chain 112 which in turn passes over a sprocket pinion 114 mounted on a shaft 116 which may be rotated, if desired, by a crank 118. It will be understood that by proper shaping of the cams 104 and proper relative location of the same rotatively about the shaft 102, the valves 60, 62, 64, and 66 may be operated in any desired sequence and with any desired intervals of time therebetween. The crank 118 may be used for manual control of the valves until the best timing conditions are ascertained and the cams 104 are properly adjusted. The valve mechanism may, if desired, be motor operated, and mechanism for this purpose is here illustrated by the electric motor 120 which drives the shaft 116 through pinion 122, gear 124, sprocket pinion 126, sprocket chain 128, and

sprocket gear 130. It will be understood by those skilled in the art that appropriate switch mechanism may be provided on shaft 102 so as to cut out motor 120 at the completion of a single revolution of shaft 102. In this manner, after the'cup 30 has had a charge of molten metal ladled into it, an operator may press a control button which in turn will start motor 120 and will put the entire machine through a single cycle of operation. At the end of that cycle, the motor 120 and the entire machine will be stopped until again manually started.

As so far described, the machine may be assumed to be in its original condition without the provision of the pressure booster mechanism. To add such mechanism, it is simply necessary to install or mount the differential piston and cylinder mechanism described in connection with Fig. 1, in an appropriate location near or on the machine, and to connect the low pressure cylinder 20 thereof to the supply line 92, 58 by means of a connection 28, as shown, and to connect the high pressure cylinder 18 thereof to the pipe line 16, 56 by means of a connection 19. With this arrangement, the operation of the booster is timed automatically, for in the normal operation of the machine, the plunger 32 is not permitted to descend until the die 2, 4 has been closed. Upon admission of pressure fluid to cylinder 50, the pressure fluid is also admitted to the low pressure cylinder 20 of the booster. As the flow of metal from cup 30 into the die begins to encounter resistance, the booster pressure is instantly built up and s applied to the disclosing cylinder 8. Thus the enormous internal force applied within and between the parting faces of the die and tending to open the same, as a result of the hydrostatic pressure of the molten metal ejected into the die under high pressure, is counteracted even as it is being developed, by the booster pressure simultaneously applied to the outside of and tending to keep the die closed.

No additional complication of the valve mechanism is needed, but one precaution must be taken care of. That precaution is to insure closing of the inlet or pressure valve 60 before the booster comes into action, for if the valve 60 is still open, theextra high pressure fluid from the booster will be permitted to back up into the regular pressure tank through pipe 12. In other words, that cam 104 which is used to control the operation of valve 60 must be appropriately shaped to permit valve 60-to close immediately afterclosing of the die, instead of being kept open until the die is ready to be opened.

It is possible to prevent this undesirable backing up of pressure from the booster by the use of a separate check valve, instead of by closing of the pressure valve 60. Such a modification of the invention is shown in Fig. 4. In this figure,

the valve box or block 10- corresponds to that mentioned in connection with Figs. 1, 2, and 3 and is similarly provided with valves 60, 62, 64, and 66. Pipes 90 and 92 are likewise connected respectively to the die operating and plunger" operating cylinders. In this case, however, the various chambers for the pair of valves 60 and 62 are completely isolated or partitioned from the chambers for the pair of valves 64 and 66, as is indicated by the dotted lines132. The supply pipe 12 from the pressure tank is branched and is admitted to each of the sets of valves through branch pipes 12' and 12". The exhaust pipe 88 is similarly connected to the exhaust tank, but is connected to the separate pairs of valves through branch pipes 88 and 88". This latter feature; 118 however, is adopted merely by way of symmetry, for it is perfectly possible for the valves to have a common exhaust chamber. Of the branches 12 and 12", the branch 12' is fitted with a check valve 134 which permits liquid flow in the direction of the arrow, that is, from the pressure tank to the valve box, but stops flow in the opposite direction. Upon reflection, it will be evident that the check valve 134 will prevent the extra high pressure fluid generated in the booster from backto that described in connection with Figs. 1, 2, 135

and 3, but supplements the mechanism there shown by providing for hydraulic closing of the valve 60 upon admission of pressure to the booster. Referring to Fig. 5 of the drawings, the valves 60 and 62 correspond to those shown in Fig. 1, as also do the supply pipe 12 and exhaust pipe 88. The pipes 90 and 92, like those shown in Fig. 1, extend to the die operating cylinder 8 and the plunger operating cylinder 50, respectively. In the present case, however, the-upper end of valve 60 is connected to a piston reciprocable in a cylinder 142 connected through a small bleeder pipe 144 to the pipe 92. With this arrangement, it will be understood that upon opening of the pressure or inlet valve 64, thereby admitting pressure fluid to pipe 92 and cylinder 50 as well as the booster, pressure is simultaneously applied to piston 140, which in turn insures closing of valve 60. This, of course, pre- 5 vents backing up of pressure generated in the booster, and insures proper application of the booster pressure to the die operating cylinder.

The normal operation of the die casting machine without the application of the booster may be divided into the following. steps. First, the die is opened and the plunger 32 is elevated, both exhaust valves 62 and 66 being open, and valves 60 and 64 being closed. Second, the die is closed, exhaust valve 62 being closed, and pressure valve 60 being opened. Valves 64 and '66 remain unchanged. Third, exhaust valve 66 is closed and pressure valve 64 is opened, thereby causing actuation of plunger 32. Valves 60and 62 meanwhile remain unchanged. Fourth, the pressure valve 64 is closed and exhaust valve 66 is opened,

thereby causing retraction of plunger 32. Valves, 60 and 62 meanwhile remain unchanged. Fifth, pressure valve 60 is closed and exhaust valve 62 is opened, thereby causing opening of the die 4. This step corresponds to'the first step, and represents the completion of the cycle. a

When the booster is added and the form of the invention utilizing a check valve is employed, as was described in connection with Fig. 4, this sequence of valve operation need not be changed in any respect, and, as was before explained, the timing of the booster is wholly automatic and takes care of itself. However, if the form of the invention described,,in connection with Figs. 1, 2, and 3 is employed, it is necessary to insure closing of valve 60, and the valve schedule therefore has added an additional step coming between the third and fourth steps outlined above. In this step, at the end of the die closing operation and 4 simultaneous with or shortly after opening of pressure valve 64, the pressure valve 60 is closed and the exhaust valve 62 is likewise kept closed. The fourth step may be left as described, that is, the pressure valve 60 may again be opened, for 5 at this time the cylinder and the booster cylinder 20 are both at exhaust, or, if desired, the pressure valve may simply be continued in its closed position. In the form of the invention described in connection with Fig. 5, similar re- 50 marks apply, for here also the valve 60 is-closed when the valve 64 is opened. It so happens, be-

cause of the nature of the cam operation described in connection with Figs. 2 and 3, that the cam for valve 60 must be cut away to permit the clos- 55 ing of valve 60, much as in the case of the arrangement shown in Fig. 1. However, it should be observed that various forms of operating mechanism may be used for the valve mechanism, an obvious variation being that in many cases the 0 valve disc 68 will be inverted and the valves will be closed, for, example, by upward movement under cam pressure, instead of by downward movement. In such case, a hydraulic interconnection of valves 64 and 60, by means of a pipe 144 such as is shown in Fig. 5, may be used to insure upward movement and closing of an inlet valve corresponding to the valve 60, immediately upon opening of an inlet valve corresponding to the valve 64, without necessitating any change whatsoever in the cams of the mechanical valve operating mechanism. From this viewpoint, the modifications herein disclosed may be broadly classified as, first, mechanical control of valve 60 to prevent backing up of the booster pressure; secondly, check valvemechanism to prevent backing up of the booster pressure; and thirdly, hydraulic operation of valve 60 to prevent backing up of the booster pressure..

It will be understood that the inventioamay be applied exactly as here described, regardless of the type of mechanism used to causeejection of transfer of molten metal into the die. For example, one broad class of die casting machines uses plunger pump mechanism which is wholly immersed or submerged in molten metal. Another class of die casting machines uses an enclosed gooseneck ladle, to the metal within which pressure, as air pressure, is directly applied. A

third class of die casting machines is like that here described, in that metal is preliminarily put into a pressure cup or receptacle, from which it is ejected by a plunger or ram. In all cases, so long as the operation of the die operating mechanism and of the metal compressing or transferring mechanism are both accomplished by means of hydrostatic pressure, the invention here described may be applied to the machine as a simple addition or accessory, with no change other than that needed to prevent backing up of the booster pressure. The mode of constructing and using the die casting mechanism of my invention, and the many advantages thereof 'will, it is thought, be apparent from the foregoing detailed description. The invention makes possible increased casting pressure without danger of opening of .the die. It makes possible increased parting face area for the mold impression in the die, without danger of opening of the die, and this in turn, when dealing with small castings, makes it possible to cast a greater number of the same at one time. The use of extraordinarily large and bulky piston and cylinder mechanism for opening and closing the die may be avoided without at the same time necessitating that the pressure under which the entire system operates be raised to an inconvenient amount. For a given range of work and pressure conditions, an extraordinary saving in power is effected, for the main bulk and volume of fluid used to close the die, or, more generally, to move the piston through most of its stroke, is fluid undermoderate pressure, and it is only at or very near the end of the stroke that the high pressure fluid is admitted,

so that this fluid is used in only small quantity. 5 But little change in the mechanism of the die casting machine is needed to add or apply my invention thereto.

It will further be apparent that while I have shown and described my invention in preferred 139 forms, many changes and modifications may be made in the structures disclosed, without departing from the spirit of the invention, defined in the following claims.

I claim:

l. A die casting machine comprising a separable die, piston and cylinder mechanism for opening and closing the die, a vessel carrying a charge of molten metal, pressure responsive means for ejecting the molten metal-from the vessel 140 into the die, a source of presure fluid, a pressure booster comprising connected pistons of small and large diameter in order to change the quantity of pressure fluid into a smaller quantity of extra high pressure fluid, means connecting the high pressure side of the booster to the die operating cylinder, means to admit pressure fluid from the source to the die operating cylinder in order to close the die, and means to thereafter connect the source of pressure fluid 1 to both the pressure responsive means and the low pressure side of the booster in order to generate and apply extra high pressure fluid in the die operating cylinder so as to keep the die tightly closed at the moment of ejection of metal into the die.

2. A die casting machine comprising a separable die, hydraulic piston and cylinder mech anism for opening and closing the die, a vessel carrying a charge of molten metal, plunger mechanism movable into the vessel for ejecting the molten metal from the vessel into the die, hydraulic piston and cylinder mechanism for operating the plunger mechanism, a source of moderate pressure fluid, a source of high pressure fluid, means to connect the source of moderate pressure fluid to the die orpeating cylinder in order to close the die, means to thereafter connect the source of moderate pressure fluid to the plunger operating cylinder in order to force molten metal into the die, means to simultaneously apply high pressure fluid in the die ophydraulic piston and cylinder mechanism for operating the plunger mechanism, a source of pressure fluid, a pressure booster comprising connected pistons of small and large diameter in order to change a quantity of pressure fluid into a smaller quantity of extra high pressure fluid, means connecting the high pressure side of the booster to the operating cylinder, means to connect the source of pressure fluid to the die operating cylinder in order to close the die, means to thereafter connect the source of pressure fluid to both the plunger operating cylinder and the low pressure side of the booster in order to force molten meltal into the die and at the same time to generate and apply extra high pressure fluid in the die operating cylinder so as to keep the die tightly closed at the moment of ejection of metal into the die, and means to prevent the extra high pressure fluid from backing up into the regular source of pressure fluid.

4. A die casting machine comprising a separable die, hydraulic cylinder and piston mechanism for opening and closing said die, a vessel carrying a charge of molten metal, pressure responsive means for ejecting the molten metal from the vessel into the die, a pressure booster,

a source of pressure fluid, valve mechanism including inlet and exhaust valves for controlling the flow of pressure fluid from the source to the die operating cylinder, and inlet and exhaust valves for controlling the flow of pressure fluid from the source to both the pressure responsive means and the low pressure side of the pressure booster, means connecting the high pressure side of the'booster to the die operating cylinder, and means for operating the aforesaid inlet and exhaust valves in proper timed sequence during each die casting operation in order to first connect the source to the die operating cylinder for closing the die, and then to connect the source to the pressure responsive means and booster in order to force metal into the die and at the same time apply extra high pressure fluid in the die operating cylinder.

5. A die casting machine comprising a separable die, hydraulic cylinder and piston mechanism for opening and closing said die, a vessel carrying a charge of molten metal, pressure responsive means for ejecting the molten metal from the vessel into the die, a pressure booster comprising directly connected reciprocable plungers of relatively large and small diameters, a source of pressure fluid, valve mechanism including inlet and exhaust valves for controlling the flow of pressure fluid from the source to the die operating cylinder, and inlet and exhaust valves for controlling the flow of pressure fluid from the source to both the pressure responsive means and the low pressure side of the pressure booster, means connecting the high pressure side of the booster to the die operating cylinder, means for operating the aforesaid inlet and exhaust valves in proper timed sequence during each die casting operation in order to first connect the source to the die operating cylinder for closing the die, then connect the source to the pressure responsive means and booster in order to force metal into the die and at the same time apply extra high pressure fluid in the die operating cylinder, and means to prevent the extra high pressure fluid from backing up into the source.

6. A die casting machine comprising a separable die, hydraulic cylinder and piston mechanism for opening and closing said die, a vessel carrying a charge of molten metal, a reciprocable plunger movable into the vessel for ejecting the molten metal from the vessel into the die, hydraulic piston and cylinder mechanism for operating said plunger, a pressure booster comprising directly connected reciprocable plungers of relatively large and small diameters, a source of pressure fluid, valve mechanism including inlet and exhaust valves for controlling the flow of pressure fluid from the source to the die operating cylinder, and inlet and exhaust valves for controlling the flow of pressure fluid from the source to both the plunger operating cylinder and the low pressure side of the pressure booster, means connecting the high pressure side of the booster to the die operating cylinder, motor driven mechanical means for operating the aforesaid inlet and exhaust valves in proper timed sequence during each die casting operation in order to first connect the source to the die operating cylinder for closing the die, then comiect the source to the plunger operating cylinder and booster in order to force metal into the die and at the same time apply extra high pressure fluid in the die operating cylinder, and means to prevent the extra high pressure fluid from backing up into the source.

7. A die casting machine comprising a receptacle for molten metal, a separable die in flow communication therewith, hydrostatic means for closing the die, hydrostatic means for ejecting metal from the receptacle into the die, a supply pipe for pressure fluid, a valve for controlling the flow of pressure fluid Irom said pipe to the hydrostatic die closing means, a valve for controlling the flow of pressure fluid to the hydrostatic metal ejecting means, a pressure booster the low pressure side of which is connected in common with the hydrostatic metal ejecting means and the high pressure side of which is connected in common with the hydrostatic die closing means, and valve control means for first opening the valve to the die closing means and for thereafter simultaneously opening the valve to the metal ejecting means and booster and closing the valve to the die closing means.

8. A die casting machine comprising a receptacle for molten metal, a separable die in flow communication therewith, hydrostatic means for closing the die, hydrostatic means for ejecting metal from the receptacle into the die, a supply pipe for pressure fluid, a valve for controlling the flow of pressure fluid from said pipe to the hydrostatic die closing means, a valve for controlling the flow oi. pressure fluid from said pipe to the hydrostatic metal ejecting means, a pressure booster the low pressure side of which is connected in common with the hydrostatic metal ejecting means and the high pressure side of which is connected in common with the hydrostatic die closing means, means to first open the valve to the die closing means and to thereafter open the valve to the metal ejecting means and booster, and an additional check valve for preventing backing up of the high pressure generated by the booster upon opening of the second valve.

9. A die casting machine comprising a receptacle for molten metal, a separable die in flow communication therewith, hydrostatic means for closing the die, hydrostatic means for ejecting metal from the receptacle into the die, a supply pipe for pressure fluid, a valve for controlling the flow of pressure fluid from said pipe to the hydrostatic die closing means. a valve for controlling the flow of pressure fluid from said pipe to the hydrostatic metal ejecting means, a pressure booster e low pressure side of which is connected in common with the hydrostatic metal ejecting means and the high pressure side of which is connected in common with the hydrostatic die closing means, and additional hydrostatic mechanism connected in common with the metal ejecting means and booster for closing the valve to the die closing means when the other valve is opened.

10. A die casting machine comprising a receptacle for molten metal, a separable die in flow communication therewith, hydrostatic means for closing the die, hydrostatic means for ejecting metal from the receptacle into the die, a supply pipe for pressure fluid, a valve for controlling the how of pressure fluid from said pipe to the hydrostatic die closing means, a valve for controlling the flow of pressure fluid from said pipe to the hydrostatic metal ejecting means, a pressure booster the low pressure side of which is connected in common with the hydrostatic metal ejecting means and the high pressure side of which is connected in common with the hydrostatic die closing means, means to first open the valve to the die closing means and to thereafter WALTER P. SHERMAN. 

